Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2017
Publication Date: 3/28/2017
Citation: Alexander, L.W., Thammina, C., Kramer, M.H. 2017. Cross-transferability of SSR markers in Osmanthus. Genetic Resources and Crop Evolution. doi:10.1007/s10722-017-0514-4.
Interpretive Summary: The genus Osmanthus consists of about 30 species of evergreen trees and shrubs distributed primarily throughout temperate and tropical China. Nursery growers wish to extend the range of Osmanthus species into more cold-hardy climates throughout both the U.S. and China. Germplasm evaluation and breeding are underway to find species and cultivars suitable for the U.S. market and incorporate favorable traits into Osmanthus through hybrid breeding. Developing a molecular tool kit for hybrid breeding of Osmanthus species and related genera is an important step in improving this species. We tested a suite of 70 SSR markers from three marker sources with the intention of determining 1) the transferability of markers within the genus, 2) the best type of marker source for transferability, and 3) genetic relationships among accessions. Transferability across taxa was high, with 67 of 70 markers transferring successfully. Forty-two of these markers led to clear size-based genotypes. Analyzing the genotypes led to the findings that 1) enriched libraries are better sources for transferable markers than sequence data, 2) molecular genetic diversity has not been impacted by breeding, and 3) an eight-marker panel can discriminate between species and cultivars. This marker panel will aid in assessing relationships and diversity within the genus Osmanthus; provide a tool for cultivar-specific identification; and provide a baseline for planning and verifying hybrid breeding.
Technical Abstract: Developing a molecular tool kit for hybrid breeding of Osmanthus species and related genera is an important step in creating a systematic breeding program for this species. To date, molecular resources have been aimed solely at O. fragrans with little work to develop markers for other species and cultivars. The objectives of this study were to 1) determine cross-transferability of O. fragrans and C. retusus derived SSRs in diverse Osmanthus taxa, 2) quantify the influence of locus-specific factors on cross-transferability, and 3) determine the genetic relationships between accessions. We tested 70 SSR markers derived from O. fragrans and Chionanthus retusus in 24 accessions of Osmanthus. Sixty-seven markers showed transfer to at least one other Osmanthus species with an overall transfer rate of 84% of loci across taxa. Genotyping with 42 microsatellite markers yielded a total of 367 loci. Number of alleles per locus ranged from 2 to 17 with a mean of 8.7 ± 4.8. Mean observed and expected heterozygosities were 0.560 ± 0.225 and 0.688 ± 0.230, respectively. Percent of polymorphic loci ranged from 40% in O. delavayi to 100% in O. fragrans. Osmanthus fragrans had the highest mean number of alleles per locus (4.2) while O. delavayi had the lowest (1.1). A reduced suite of eight-markers can distinguish between accessions with a probability of identity from 3.91E-04 to 2.90E-07. Evaluation of more Osmanthus and Chionanthus accessions and subsequent hybridizations will be necessary to introgress favorable genes and generate the variation necessary to expand the genus into new markets. The SSR markers described herein will be immediately useful to characterize germplasm, identify hybrids, and aid in understanding the level of genetic diversity and relationships within the cultivated germplasm.